FIG. 1 shows a prior-art data communication system 100 used for connecting to base stations 101, 102, and 103 of a mobile telephone network. The data communication system includes data communication devices 104, 105, 106, and 107, which may by e.g. IP (Internet Protocol) routers, multiprotocol label switches (MPLS) and/or Ethernet switches. Each data communication device may consist of a single apparatus or a combination of a plurality of apparatuses. The data communication devices are interconnected through a regional data communication network 108. The data communication network 108 includes other data communication devices and data communication links between them. The data communication system includes a gateway device 109 providing a connection to a data communication backbone network 110, represented e.g. by the global internet. The gateway device 109 is connected through a data communication device 107 to the regional data communication network 108. The data communication system includes a mobility management entity (MME) 111 which is arranged to maintain up-to-date information about the locations of terminals 112, 113, and 114 in the radio communication network comprised of base stations 101 to 103. The mobility management entity 111 is connected to the gateway device 109 either directly or through the data communication network. The mobility management entity 111 may also be embedded in the gateway device 109. Each of the terminals 112, 113, and 114 could be a mobile phone or a palmtop computer, for example. The mobility management entity 111 is arranged to produce control data based on the locations of terminals 112 to 114 so that data communication devices 104 to 107 and the gateway device 109 are able to form logical data communication tunnels 115, 116, and 117 between the base stations 101, 102, and 103 and the gateway device 109. Such logical data communication tunnels may be e.g. GTP-U (General Packet Radio Service Tunneling Protocol-User plane messages) tunnels, GRE (Generic Routing Encapsulation) tunnels, IpinIP (Internet Protocol in Internet Protocol) tunnels or data communication tunnels implemented using Ethernet frames.
In the situation depicted in FIG. 1 we can assume, for example, that terminal 112 is in the coverage area of base station 101, terminal 113 is in the coverage area of base station 102, and terminal 114 is in the coverage area of base station 103. We can further assume that the data of terminal 112 is transferred in the logical data communication tunnel 115, the data of terminal 113 is transferred in the logical data communication tunnel 116, and the data of terminal 114 is transferred in the logical data communication tunnel 117. If, for example, terminal 112 moves from the coverage area of base station 101 into the coverage area of base station 102, the logical data communication tunnel 115 is removed and a corresponding new logical data communication tunnel is formed between the gateway device 109 and base station 102. The problem with the data communication system 100 described above is that the data traffic from and to the terminals travels through the gateway device 109. In other words, the data traffic from and to the terminals must go through a single point in the data communication network. Therefore, the regional data communication network 108, the data communication device 107, and the gateway device 109 may come under a very heavy load, which has to be taken into consideration when designing data communication links and data communication devices.